This Melissa and Doug train puzzle was another $5 resale shop find that I'm very pleased with. The boys love trains, and A (age 4) was very excited to put the puzzle together. It was not as easy for him as I thought it would be, but with some encouragement he finished the entire puzzle (singing the ABC song a few times as he worked). J is very fond of the engine puzzle piece and we almost lost it because he insisted on carrying it around the house. (I was extremely relieved to find it in the sofa this morning.) The puzzle is big, it says 10 feet long, but it fit diagonally across our small family room floor with room to spare.
Here's a link to the puzzle at Amazon:
FLOOR PUZZLE ALPHABET TRAIN
It's a better value paired with a firetruck puzzle
Alphabet Train and Giant Fire Truck Floor Puzzle Assortment
Amazon has several kinds of train floor puzzles available.